This invention relates to papermaker's fabrics and in particular to fabrics used on the wet press section of a papermaking machine.
Papermaker's wet felts are designed to transport an aqueous web of paper through the press rollers of a papermaking machine and to assist in the de-watering thereof. In one form, a papermaker's wet felt is constructed from a woven base fabric having batts needled to one or both sides.
The amount of void volume within the base fabric of a wet felt is directly related to the amount of water which can be handled internally to the felt while in the nip. In other words, felts which can run with a "dry nip" (no water puddling behind the nip) are less likely to result in crushing or other hydraulic phenomena. It has been recognized in the art that it is possible to maintain a desired controlled void volume within the fabric construction by employing multi-layered base fabrics. One example of such a felt is disclosed in U.S. Pat. No. 4,356,225 which is assigned the assignee of the present invention. Other examples are also cited in that patent.
The surfaces of the base fabric of such conventional fabrics are predominantly defined by the top and bottom layers of machine direction yarns. The cross machine direction yarns which interweave the multiple layers of machine direction yarns of such fabrics protrude beyond the surfaces of the base fabric with sharp infrequent knuckles. It has been discovered that under the intense pressure of the nip, water removal can be impaired by the extremes of high and low pressure caused by the cross-machine direction yarn knuckles on the paperbearing side of the fabric. Also, on the other side of the fabric, the knuckles represent high pressure points which result in accelerated wear of the fabric.